A paint calculator takes the guesswork out of buying interior paint by estimating exactly how many gallons you need based on your room dimensions. It accounts for doors, windows, and the number of coats, so you buy the right amount — no wasted trips to the store and no leftover cans cluttering your garage. Enter your measurements below and get an instant paint estimate with cost breakdown.
Room Paint Estimator
Paint Settings
Project Breakdown
How to Use the Paint Calculator
Estimating how much paint to buy is one of the trickiest parts of any interior painting project. Buy too little and you are making an extra trip to the store mid-project. Buy too much and you have leftover cans collecting dust. This paint calculator eliminates the guesswork by computing the exact number of gallons you need based on your room dimensions, accounting for doors, windows, coats, and coverage rate.
Step 1: Enter Room Dimensions
Start by entering the length, width, and height of the room you want to paint. The calculator computes the total wall area by multiplying the perimeter (2 x length + 2 x width) by the ceiling height. If you prefer to work in meters rather than feet, click the "Meters" button at the top to switch units — the calculator automatically converts for accurate results.
Step 2: Subtract Doors and Windows
Enter the number of standard doors and windows in the room. Each door subtracts approximately 21 square feet and each window subtracts approximately 15 square feet from the paintable area. This adjustment ensures you are not buying paint for surfaces you will not actually be covering, which can save you money on larger rooms with multiple openings.
Step 3: Choose Coats and Coverage
Select whether you need one or two coats of paint. Two coats is the standard recommendation for most interior projects, especially when changing colors or painting over a dark surface. You can also adjust the coverage rate — most interior latex paints cover about 350 square feet per gallon, but premium paints may cover up to 400 square feet. Check your paint can label for the manufacturer's recommended coverage.
Step 4: Add Multiple Rooms
If you are painting more than one room, click "Add Another Room" to include additional spaces in your calculation. Each room can have different dimensions and door/window counts. The calculator sums everything and provides a combined total, making it easy to plan a whole-house painting project in one step.
Step 5: Review Results and Cost
The results section shows four key metrics: total wall area, paintable area (after subtracting doors and windows), gallons needed (rounded up to the nearest whole gallon), and estimated cost. Enter your price per gallon to see the total material cost for your project. The detailed breakdown below shows exactly how each number was calculated, so you can verify the estimate and adjust as needed.
FAQ
Is this paint calculator free?
Yes, this paint calculator is completely free with no hidden fees, no signup, and no limits. You can calculate paint for as many rooms as you like. Everything runs in your browser — your data stays on your device.
Is my data private when I use this tool?
Absolutely. All calculations run entirely in your browser using client-side JavaScript. No room dimensions, project details, or personal data are ever sent to a server. Your information stays completely private on your device.
How much paint do I need for a 10x12 room?
A typical 10x12 room with 8-foot ceilings has about 352 square feet of wall area. After subtracting a standard door and window, the paintable area is roughly 316 square feet. At 350 sq ft per gallon coverage, you need about 1 gallon for one coat or 2 gallons for two coats. This calculator handles this math instantly.
How many coats of paint do I need?
Most interior paint jobs require two coats for even, complete coverage — especially when changing colors. One coat may suffice if you are repainting the same color with high-quality paint. This calculator defaults to two coats but lets you switch to one for quick touch-up estimates.
What does paint coverage rate mean?
Paint coverage rate is the area one gallon of paint covers in a single coat, measured in square feet per gallon. Most interior latex paints cover 350-400 sq ft per gallon. Premium paints may cover more, while textured surfaces require more paint. The default of 350 sq ft/gallon is a safe estimate for most projects.
Should I subtract doors and windows from my wall area?
Yes. Standard doors are approximately 21 square feet and standard windows about 15 square feet. Subtracting these gives you a more accurate paintable area and prevents buying excess paint. This calculator automatically deducts the correct amount based on the number of doors and windows you enter.
Can I calculate paint for multiple rooms at once?
Yes, click the 'Add Room' button to add as many rooms as needed. Each room can have different dimensions, door and window counts. The calculator totals everything and shows you the combined gallons needed and total cost estimate for your entire project.
How do I switch between feet and meters?
Use the unit toggle at the top of the calculator to switch between feet and meters. All dimension labels update automatically. Internally the calculator converts meters to feet for the paint coverage calculation, since paint coverage is rated in square feet per gallon.